1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a duplexer and a fabrication method, and more particularly to a monolithic duplexer that can obtain a high isolation between elements integrated on a single chip and fabrication method thereof.
2. Description of the Related Art
A duplexer properly splits signals transmitted and received through a single antenna in a communication system using a frequency division system such that one antenna can effectively be shared.
The duplexer basically comprises a transmitter filter and a receiver filter. The transmitter filter is a band pass filter which passes only a signal in a frequency band for transmission, and the receiver filter is a band pass filter which passes only a signal in a frequency band for reception. Signals only in a certain frequency band can pass the filters so that one antenna can be effectively shared. The duplexer is mainly applied to various radio frequency (RF) devices performing wireless communication.
Since a difference between the frequencies of the signals transmitted and received through the transmitter filter and the receiver filter is small, the signals are quite sensitive to inter-signal interference. Accordingly, the duplexer can have improved performance by adding an isolation part which can prevent the inter-signal interference by isolating the transmitter filter and the receiver filter from each other. The isolation part implements a phase shifter using a capacitor and an inductor to prevent the inter-signal interference by making the phase difference between the frequencies of the transmitted signal and the received signal substantially at 90 degrees.
As the use of mobile communication devices, such as mobile phones, increases, the demand for miniaturized and lightweight duplexers for the devices has increased. Additionally, the demand for miniaturized and lightweight filters performing as the transmitter filter and receiver filter, which are component parts of the duplexer, has increased. A film bulk acoustic resonator (FBAR) is known as a means for a filter which is miniaturized, lightweight and suitable for electric force. The FBAR can be mass-produced at a minimum cost and can be implemented in a minimum size.
The duplexer is required to be miniaturized and lightweight due to the miniaturization of mobile phones; however, it is difficult to obtain high isolation as the duplexer becomes miniaturized. Accordingly, a micro duplexer is required which is miniaturized, lightweight, and capable of obtaining a high isolation.